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Changes in oxytocin receptor mRNA in the rat uterus measured by competitive reverse transcription-polymerase chain
C X Liu1, S Takahashi, T Murata
1Department of Physiology, Kochi Medical School, Japan.
Abstract:
Large changes in the responsiveness of target organs to oxytocin are thought to originate from alteration of the number of oxytocin receptors (OTR). To elucidate the molecular mechanisms regulating the synthesis of the OTR, we developed a competitive reverse transcription-PCR protocol to measure OTR mRNA. We synthesized cRNA comprising a small stuffer introduced into the target mRNA. Using this cRNA as an internal standard, we made a quantitative estimation of OTR mRNA. Application of this method to the rat uterus revealed that the mean levels of OTR mRNA remained unchanged until 1030-1100 h on day 21 of pregnancy, increased significantly after 2200-2230 h on the same day and declined rapidly after parturition. A similar rapid increase in uterine OTR mRNA content was observed in rats given prostaglandin on day 18, inducing premature delivery on day 19 of pregnancy. All parturient rats had higher OTR mRNA levels regardless of whether parturition was spontaneous or prostaglandin induced. However, in a few rats, OTR mRNA remained as low as that observed during mid pregnancy even on day 22 of gestation, the expected day of parturition in about 70% of the rats in our colony. A similar increase in uterine OTR mRNA content to that observed at parturition was induced by oestrogen treatment for 3 days in ovariectomized virgin rats, but concomitant injection of progesterone did not influence the effect of oestrogen. The present results revealed that the large increase of uterine OTR at the peripartum period is accompanied by an increase in OTR mRNA content that may be brought about, at least in part, by increased oestrogen secretion following luteolysis.
Insights
The study found that oxytocin receptor (OTR) mRNA levels in the rat uterus significantly increase around the time of parturition. This increase is linked to estrogen secretion and may be induced by prostaglandins or estrogen treatment.
Area of Science:
- Reproductive biology
- Molecular endocrinology
- Gene expression regulation
Background:
- Oxytocin receptor (OTR) number changes are linked to target organ responsiveness.
- Understanding OTR synthesis regulation is crucial for reproductive physiology.
Purpose of the Study:
- To elucidate molecular mechanisms regulating oxytocin receptor (OTR) synthesis.
- To quantify OTR mRNA levels in the rat uterus during pregnancy and parturition.
Main Methods:
- Developed a competitive reverse transcription-PCR protocol for OTR mRNA quantification.
- Utilized synthesized cRNA as an internal standard for accurate measurement.
- Applied the method to rat uteri during late pregnancy, parturition, and after prostaglandin induction.
Main Results:
- Uterine OTR mRNA levels remained stable until late pregnancy day 21, then increased significantly before parturition.
- Prostaglandin-induced premature delivery also led to a rapid increase in OTR mRNA.
- Estrogen treatment in ovariectomized rats mimicked the periparturient increase in OTR mRNA.
Conclusions:
- The periparturition surge in uterine OTR is associated with increased OTR mRNA levels.
- Increased estrogen secretion following luteolysis likely contributes to the rise in OTR mRNA.
- This study provides molecular insights into OTR regulation during the critical peripartum period.
